An inkjet printer is used as a device for outputing images processed by a computer or images captured by a digital camera. An inkjet printer forms dots by ejection of ink of various colors such as cyan, magenta, yellow and black, for example. Dots of each color are typically ejected from a print head while the print head is moving in a main scanning direction. If the positions at which the dots of each color are formed are misaligned, it would cause a problem of reduced image quality.
This problem of image quality deterioration due to dot formation misalignment occurs in both uni-directional recording and bi-directional recording. Here, uni-directional recording refers to a recording method in which, where the print head moves back and forth along the main scanning passes, the dots are ejected only when the print head is moving along one of the passes. Bi-directional printing refers to a recording method in which dots are ejected when the print head is moving along both of the main scanning passes. While the problem of dot position misalignment typically occurs with respect to dots of different colors in uni-directional printing, it occurs in bi-directional printing with respect to dots of the same color formed during forward and reverse passes.
In the conventional printer, the dot position misalignment may be reduced by adjusting the formation positions of color dots in the main scanning direction while using black dots as a reference, for example. This type of dot position misalignment adjustment is realized by a head drive circuit that supplies drive signals to the print head while changing the output timing of the drive signals.
However, the above-described conventional dot position misalignment adjustment method has various inherent limitations. For example, because the drive signal timing can be changed only for the entire print head in a typical printer, dot position misalignment adjustment is limited to what can be achieved by the timing change.
The present invention was made in order to resolve the abovementioned problem with the conventional art, and an object thereof is to provide the technique that reduces the dot position misalignment in the main scanning direction using a means other than changing the drive signal output timing from the head drive circuit, thereby improving image quality.